“The reason the wing of a bat and the arm of a human share a common skeletal pattern is because they shared a common ancestor. The same reasoning applies to human arms and bird wings, human legs and frog legs- everything that has limbs. There is a major difference between Owen’s theory and that of Darwin: Darwin’s theory allows us to make very precise predictions” (Shubin 32).
This excerpt concentrates on different methods of constructing phylogenies. For example, fossil evidence supports the fact that bats forelimbs and bird wings arose independently from walking forelimbs of different ancestors. Therefore, the bat’s forelimb is “homologous to those of other animals, but analogous in function to a bird’s wing” (1).
Furthermore, this excerpt focuses on Darwin’s theory of evolution. Darwin developed multiple ideas critical to the advancement of biology, and one of these is commonly known as evolution. Darwin believed that over millions of years, as a species spread over various habitats throughout the world, it accumulated a variety of adaptations. This “accumulation” occurred as a result of a process now known as natural selection. According to Darwin, “in each generation, environmental factors filter heritable variations, favoring some over others” (1). In this case, both a bat and a human are taxonomically similar, as they are both of the phyla Chordata. However, humans are primates, while bats are of the order chiroptera. Both are vertebrates and endothermic organisms, but humans are phylogenetically more evolved than bats. One characteristic that sets the two apart is terrestrial bipedalism.
Evolution is only possible because of genetic variation. Variation in gene pools occurs because of both mutation and sexual recombination. During a genetic mutation, the nucleotide sequence of DNA is altered. However, “it is not possible to predict how it will alter DNA and what its effects will be” (1). As the majority of mutations occur in somatic cells, they are impossible to pass on to offspring. Only the mutations that occur in the gametes of an organism may be passed on. Variations because of gene duplication have played a major role in evolution, far greater than point mutations. Even more important than mutation to evolution is sexual recombination (1). Because of the numerous possible combinations of mating partners in a gene pool, offspring will have alleles that have been rearranged into fresh combinations.
While this excerpt makes sense scientifically, it seems fairly simplistic in comparison to the text we have studied from over the course of this year. This makes sense, as this scientific book was published with the common public as an audience, and not biology students. It is possible that the author has not yet developed any key concepts in the book, and it will become more complex.
Works Cited
(1) Campbell, Neil A., and Jane B. Reece. Biology. San Francisco: Pearson, Benjamin Cummings, 2005. Print. Post #2
"At conception, we start as a single cell that contains all the DNA needed to build our body. The plan for that entire body unfolds via the instructions contained in this single microscopic cell" (46)
In order to sexually reproduce, a male and female organism must produce reproductive cells known as gametes in their gonads. The production of these cells occurs in a process known as meiosis. Meiosis occurs in two phases- meiosis I and meiosis II. During interphase, the chromosomes of a diploid cell replicate. Then, during prophase I, the chromosomes condense. One pairs of sister chromatids, known as a tetrad, undergoes a process known as “crossing over”, where the “DNA molecules of nonsister chromatids break at corresponding places and then rejoin to the other’s DNA” (2, 244). Then, in metaphase I, each tetrad arranges on the metaphase plate. During anaphase I, the tetrads are split, but the sister chromatids remain together, and move towards opposite ends of the cell. Then, in telophase I and cytokinesis, either a cleavage furrow or cell plate forms, and the cytoplasm splits, dividing the cell into two. Then, during Meiosis II, the same stages occur. In prophase II, a spindle apparatus is formed, and the chromosomes (still as sister chromatids) move towards the metaphase plate. During metaphase II, the sister chromatids are positioned on the metaphase plate- each of the individual chromatids is not genetically identical, because of crossing over in meiosis I. In Anaphase II, the sister chromatids are pulled apart, and move towards opposite poles of the cell. Then, in telophase II and cytokinesis, the nuclei reform and the chromosomes decondense. The cytoplasm is split in two for each cell, and four haploid daughter cells, each genetically distinct, are formed. The genetic variation between the four daughter cells is critical, as without it, evolution would occur on a much less broad scale. Only mutations would be responsible for genetic variation.
Once daughter cells are produced in an organism, sexual reproduction and fertilization may occur. In humans, a haploid gamete has 23 chromosomes, and therefore only has a single chromosome set. A diploid zygote for humans, on the other hand, contains 46 chromosomes and therefore has two chromosome sets (2, 241). In sexual reproduction, a haploid sperm from the father fuses with a haploid ovum from the mother. When two gametes fuse, their nuclei fuse as well, in a process known as fertilization. A fertilized egg is known as the zygote, and it is diploid. While mitosis generates the somatic cells of the body, meiosis generates the gametes, and the cycle continues when gametes fuse again. Only the genes in the genetically varying gametes are passed on to offspring- somatic cells, which are identical, are not involved in reproduction.
Because of errors during meiosis, a variety of genetic disorders may occur. For example, in nondisjunction, “the members of a pair of homologous chromosomes do not move apart properly during meiosis I, or sister chromatids fail to separate during meiosis II” (2, 285). If during fertilization, one of the abnormal gametes fuses with one that is normal, the offspring will have abnormal numbers of particular chromosomes, known as aneuploidy. Aneuploidy of multiple chromosomes often results in prenatal death (1). In monosomic aneuploidy, one of a pair of chromosomes is missing. One disease caused by this nondisjunction is Monosomy X, also known as Turner syndrome. Women who have this disease are “phenotypically female” but are “sterile because their sex organs do not mature” (2, 287). In trisomic aneuploidy, there are three of a particular chromosome. Trisomy 21, or trisomy of the 21st chromosome, is more commonly known as Down Syndrome. It is common that those with Down Syndrome have “characteristic facial features, short stature, heart defects…and mental retardation” (2, 287).
As Neil Shubin states, each person begins as a single cell, and the DNA of that cell may build an entire body. However, all too often, the plan for that body may go seriously awry. Once again, Shubin presents his readers with an oversimplified biological description, in this case of sexual reproduction. However, this is fitting for his generally paleontological book.
Works Cited (1) "Aneuploidy and Deletions." Arbl.cvmbs.colostate.edu. Web. 31 May 2010. <http://www.vivo.colostate.edu/hbooks/genetics/medgen/chromo/aneuploidy.html>.
(2) Campbell, Neil A., and Jane B. Reece. Biology. San Francisco: Pearson, Benjamin Cummings, 2005. Print. Post #3
"The bumps, pits, and ridges on teeth often reflect the diet. Carnivores, such as cats, have blade-like molars to cut meat, while plant eaters have a mouth full of flatter teeth that can macerate leaves and nuts" (60).
This excerpt clearly relates to the major theme of biology- the relationship of structure to function. Evolutionarily, the anatomical features of herbivores seem more recently evolved than those of carnivores. The differences between these two types of consumers occur primarily in the region of the oral cavity. It has been noted that “herbivorous mammals have well-developed facial musculature, fleshy lips, a relatively small opening into the oral cavity and a thickened, muscular tongue”(3). All of these features have a structure that directly correlates to function- for example, the muscular tongue of herbivores aids in the chewing of cellulose. However, the structure of the teeth of these organisms seem most adapted to their function, and also reflect their diet. Depending on the specific type of vegetation a species has adapted to eat, their dentition will vary significantly. However, it is common that “the teeth of herbivorous animals are closely grouped so that the incisors form an efficient cropping/biting mechanism” (3). Furthermore, the herbivore incisors are broad and flattened, while the molars are square and flattened. The function of both of these teeth is to provide a grinding surface for food, as well as to crush and grind the food itself. The methodical grinding of food in herbivores is a process necessary to disrupt the plant cells walls in order to release digestible intracellular contents.
The teeth of carnivores also tend to fit the biological theme of the relationship of structure to function. The teeth of carnivores tend to be either conical or triangular, in order to pierce flesh. More specifically, animals such as snakes, that swallow their food whole, tend to have conical teeth. Prey items can then be grabbed and held inside the mouth. However, carnivores such as sharks, which saw of chucks of meat to obtain food, have triangular teeth with serrations (4).
This quote also relates to the digestive system, as the oral cavity is the beginning of both physical and chemical digestion of food. In the oral cavity, ducts secrete saliva, which contains salivary amylase (2). This enzyme “hydrolyzes starch…and glycogen”. Ultimately, the mastication of food helps to amplify the process of the chemical digestion of carbohydrates in the mouth.
This excerpt also may be related to the evolution of human jaws and teeth. Because of the change in human diet from one that was course and abrasive to a softer more westernized palate, evolutionists have determined that the human jaw has grown smaller, creating less room for teeth. Ultimately, “evolution has produced an increase in brain size at the expense of jaw size” (1). Therefore, there is often less room in the mouth for the wisdom teeth, also known as the third molars. These teeth are now regarded as vestigial, as they are generally useless to those who have them.
Once again, Shubin is able to take a topic that may seem quite difficult to understand, such as the reasoning behind differences in the structure of organisms, and oversimplify it for the average person to understand. However, this excerpt fails to mention that there are numerous variances in structure between two organisms that are both carnivores or both herbivores, simply because of varying niches and food sources.
"Like us, fish, lizards, and cows have bodies that are symmetrical with a front/back, top/bottom, and left/right. Their front ends (corresponding to the top of an upright human) all have heads, with sense organs and brains inside. They have a spinal chord that runs the length of the body along the back. Also like us, they have an anus, which is at the opposite end of their bodies from the mouth" (97).
This excerpt relates directly back to our dissection lab, where we determined the physical characteristics of animals, such as symmetry, cephalization, and tissue layers. We also focused on whether animals were coelomates or acoelomates- that is, whether or not they had a body cavity, as well as the structure of their digestive systems. These two final properties relate back to the mode of development of animals.
Animals may either develop as protostomes or deuterostomes. These modes are generally distinguished by three features- cleavage, coelom formation, and fate of the blastopore. In animals with protostomes development, such as an earthworm, a pattern known as spiral cleavage is often seen. This type of cleavage is often known as “determinate cleavage”, because the pattern of development may determine the development of the embryonic cell very early on. In contrast, animals with deuterostomes development, such as humans, tend to develop in a pattern known as radial cleavage. In this type of cleavage, which is indeterminate, “each cell produced by early cleavage divisions retains the capacity to develop into a complete embryo” (1). In both protostomes and deuterostomes, the digestive system begins as a pouch known as the archenteron. However, in protostomes, the mesoderm splits to form the ceolom. However, in deuterostomes the folds of the archenteron form the coeloms. Ultimately, the most distinguishable characteristic that differentiates protostome development and deuterostome development is the fate of the blastopore. The blastopore is “the indentation that during gastrulation leads to the formation of the archenteron” (1). After the development of the archenteron, another opening develops at the other end of the gastrula. These two openings become the mouth and anus of the organism. In protostomes, the blastopore becomes the mouth, while in deuterostomes, the blastopore develops into the anus.
In our phylogenetic trees, one of the indications for the evolution of organisms was deuterostomes versus protostomes. The animals that are acoelomates are also protostomes, while the animals that are coelomates are also deuterostomes. Animals with a coelom tend to be more “evolved” than those without one- these animals included the rat, snake, frog, and perch. Therefore, the connection can be made that deuterostome development generally leads to animals that are more evolved.
Only at this point in Niel Shubin's book have I started to appreciate his ability of relating science to daily life. My thought process prior to this moment was that Shubin's supposedly "scientific" explanations of animal structure and evolution were actually insufficient in their scientific support. However, I have come to the conclusion (finally!) that Shubin does a remarkable job at simplifying almost every topic in his book. The way he relates and appeals to the reader by stating "like us" makes it even simpler to understand these scientific concepts (although they're pretty simple in the first place)....Actually, now that I think about it, I think this guy should stick to digging up bones.
Works Cited
(1) Campbell, Neil A., and Jane B. Reece. Biology. San Francisco: Pearson, Benjamin Cummings, 2005. Print. Post # 5
"When the finely tuned balance among the different parts of bodies breaks down, the individual creature can die. A cancerous tumor, for example, is born when one batch of cells no longer cooperates with others. By dividing endlessly, or by failing to die properly, these cells can destroy the necessary balance that makes a living individual person" (118).
The human body is a finely tuned machine, where every individual part must work in harmony in order for there to be proper function. However, as the excerpt above mentions, it is quite possible that very minor errors could lead to life altering (or even life ending) cell malfunctions. Cancerous activity in the body is caused by mutation- whether these mutations are just spontaneous genetics or the result of environmental influences (chemical carcinogens, X-rays, viruses, etc.) is up to “luck”. However, these mutations must occur in the somatic cells of the body, which divide and multiply by mitosis, rather than in gametes.
Cancer in the body may also be caused by specific cancer causing genes called Oncogenes. Normal cellular genes that “code for proteins that stimulate normal cell growth and division” (1) are known as Proto- Oncogenes. However, Proto-oncogenes may become cancer causing oncogenes because of various genetic changes that may lead to overproduction of a proto-oncogenes protein product, or problems “in the intrinsic activity of each protein molecule” (1). Once a cell undergoes transformation, and then evades destruction by the immune system, it may then form a tumor, which is a mass of these abnormal cells.
The results of any of these causes of cancer are density independent and anchorage independent cancer cells, with a loss of cell cycle controls (see video above for an excellent explanation of these two topics) . When cancer cells do stop dividing, they do not do so at the normal checkpoints of the cell cycle. However, cancerous cells (when provided with ample nutrients) are said to be immortal. For instance, the cancerous cells removed from Henrietta Lacks as a tumor containing stem cells have been reproducing since 1951. A tumor is considered benign when it remains at its original site, but it is malignant when it becomes invasive to other organs of the body as it travels by means of metastasis.
After reading this excerpt, and learning about the causes of cancer in depth, I have realized just how difficult it must be for scientists to research potential cures. The fact that there are so many causes of cancer (some of them probably still unidentified) must make it seem nearly impossible to find a cure. We all see foundations such as the Jimmy Fund in local supermarkets, asking for donations for cancer research, and many often walk by without donating even a dollar. Scientists must feel such pressure from society when they are searching for cures from diseases, especially when they are very common.
Works Cited
(1) Campbell, Neil A., and Jane B. Reece. Biology. San Francisco: Pearson, Benjamin Cummings, 2005. Print.
by Neil Shubin
Post #1
“The reason the wing of a bat and the arm of a human share a common skeletal pattern is because they shared a common ancestor. The same reasoning applies to human arms and bird wings, human legs and frog legs- everything that has limbs. There is a major difference between Owen’s theory and that of Darwin: Darwin’s theory allows us to make very precise predictions” (Shubin 32).
This excerpt concentrates on different methods of constructing phylogenies. For example, fossil evidence supports the fact that bats forelimbs and bird wings arose independently from walking forelimbs of different ancestors. Therefore, the bat’s forelimb is “homologous to those of other animals, but analogous in function to a bird’s wing” (1).
Furthermore, this excerpt focuses on Darwin’s theory of evolution. Darwin developed multiple ideas critical to the advancement of biology, and one of these is commonly known as evolution. Darwin believed that over millions of years, as a species spread over various habitats throughout the world, it accumulated a variety of adaptations. This “accumulation” occurred as a result of a process now known as natural selection. According to Darwin, “in each generation, environmental factors filter heritable variations, favoring some over others” (1). In this case, both a bat and a human are taxonomically similar, as they are both of the phyla Chordata. However, humans are primates, while bats are of the order chiroptera. Both are vertebrates and endothermic organisms, but humans are phylogenetically more evolved than bats. One characteristic that sets the two apart is terrestrial bipedalism.
Evolution is only possible because of genetic variation. Variation in gene pools occurs because of both mutation and sexual recombination. During a genetic mutation, the nucleotide sequence of DNA is altered. However, “it is not possible to predict how it will alter DNA and what its effects will be” (1). As the majority of mutations occur in somatic cells, they are impossible to pass on to offspring. Only the mutations that occur in the gametes of an organism may be passed on. Variations because of gene duplication have played a major role in evolution, far greater than point mutations. Even more important than mutation to evolution is sexual recombination (1). Because of the numerous possible combinations of mating partners in a gene pool, offspring will have alleles that have been rearranged into fresh combinations.
While this excerpt makes sense scientifically, it seems fairly simplistic in comparison to the text we have studied from over the course of this year. This makes sense, as this scientific book was published with the common public as an audience, and not biology students. It is possible that the author has not yet developed any key concepts in the book, and it will become more complex.
Works Cited
(1) Campbell, Neil A., and Jane B. Reece. Biology. San Francisco: Pearson, Benjamin Cummings, 2005. Print.
Post #2
"At conception, we start as a single cell that contains all the DNA needed to build our body. The plan for that entire body unfolds via the instructions contained in this single microscopic cell" (46)
In order to sexually reproduce, a male and female organism must produce reproductive cells known as gametes in their gonads. The production of these cells occurs in a process known as meiosis. Meiosis occurs in two phases- meiosis I and meiosis II. During interphase, the chromosomes of a diploid cell replicate. Then, during prophase I, the chromosomes condense. One pairs of sister chromatids, known as a tetrad, undergoes a process known as “crossing over”, where the “DNA molecules of nonsister chromatids break at corresponding places and then rejoin to the other’s DNA” (2, 244). Then, in metaphase I, each tetrad arranges on the metaphase plate. During anaphase I, the tetrads are split, but the sister chromatids remain together, and move towards opposite ends of the cell. Then, in telophase I and cytokinesis, either a cleavage furrow or cell plate forms, and the cytoplasm splits, dividing the cell into two. Then, during Meiosis II, the same stages occur. In prophase II, a spindle apparatus is formed, and the chromosomes (still as sister chromatids) move towards the metaphase plate. During metaphase II, the sister chromatids are positioned on the metaphase plate- each of the individual chromatids is not genetically identical, because of crossing over in meiosis I. In Anaphase II, the sister chromatids are pulled apart, and move towards opposite poles of the cell. Then, in telophase II and cytokinesis, the nuclei reform and the chromosomes decondense. The cytoplasm is split in two for each cell, and four haploid daughter cells, each genetically distinct, are formed. The genetic variation between the four daughter cells is critical, as without it, evolution would occur on a much less broad scale. Only mutations would be responsible for genetic variation.
Once daughter cells are produced in an organism, sexual reproduction and fertilization may occur. In humans, a haploid gamete has 23 chromosomes, and therefore only has a single chromosome set. A diploid zygote for humans, on the other hand, contains 46 chromosomes and therefore has two chromosome sets (2, 241). In sexual reproduction, a haploid sperm from the father fuses with a haploid ovum from the mother. When two gametes fuse, their nuclei fuse as well, in a process known as fertilization. A fertilized egg is known as the zygote, and it is diploid. While mitosis generates the somatic cells of the body, meiosis generates the gametes, and the cycle continues when gametes fuse again. Only the genes in the genetically varying gametes are passed on to offspring- somatic cells, which are identical, are not involved in reproduction.
Because of errors during meiosis, a variety of genetic disorders may occur. For example, in nondisjunction, “the members of a pair of homologous chromosomes do not move apart properly during meiosis I, or sister chromatids fail to separate during meiosis II” (2, 285). If during fertilization, one of the abnormal gametes fuses with one that is normal, the offspring will have abnormal numbers of particular chromosomes, known as aneuploidy. Aneuploidy of multiple chromosomes often results in prenatal death (1). In monosomic aneuploidy, one of a pair of chromosomes is missing. One disease caused by this nondisjunction is Monosomy X, also known as Turner syndrome. Women who have this disease are “phenotypically female” but are “sterile because their sex organs do not mature” (2, 287). In trisomic aneuploidy, there are three of a particular chromosome. Trisomy 21, or trisomy of the 21st chromosome, is more commonly known as Down Syndrome. It is common that those with Down Syndrome have “characteristic facial features, short stature, heart defects…and mental retardation” (2, 287).
As Neil Shubin states, each person begins as a single cell, and the DNA of that cell may build an entire body. However, all too often, the plan for that body may go seriously awry. Once again, Shubin presents his readers with an oversimplified biological description, in this case of sexual reproduction. However, this is fitting for his generally paleontological book.
Works Cited
(1) "Aneuploidy and Deletions." Arbl.cvmbs.colostate.edu. Web. 31 May 2010. <http://www.vivo.colostate.edu/hbooks/genetics/medgen/chromo/aneuploidy.html>.
(2) Campbell, Neil A., and Jane B. Reece. Biology. San Francisco: Pearson, Benjamin Cummings, 2005. Print.
Post #3
"The bumps, pits, and ridges on teeth often reflect the diet. Carnivores, such as cats, have blade-like molars to cut meat, while plant eaters have a mouth full of flatter teeth that can macerate leaves and nuts" (60).
This excerpt clearly relates to the major theme of biology- the relationship of structure to function. Evolutionarily, the anatomical features of herbivores seem more recently evolved than those of carnivores. The differences between these two types of consumers occur primarily in the region of the oral cavity. It has been noted that “herbivorous mammals have well-developed facial musculature, fleshy lips, a relatively small opening into the oral cavity and a thickened, muscular tongue”(3). All of these features have a structure that directly correlates to function- for example, the muscular tongue of herbivores aids in the chewing of cellulose. However, the structure of the teeth of these organisms seem most adapted to their function, and also reflect their diet. Depending on the specific type of vegetation a species has adapted to eat, their dentition will vary significantly. However, it is common that “the teeth of herbivorous animals are closely grouped so that the incisors form an efficient cropping/biting mechanism” (3). Furthermore, the herbivore incisors are broad and flattened, while the molars are square and flattened. The function of both of these teeth is to provide a grinding surface for food, as well as to crush and grind the food itself. The methodical grinding of food in herbivores is a process necessary to disrupt the plant cells walls in order to release digestible intracellular contents.
The teeth of carnivores also tend to fit the biological theme of the relationship of structure to function. The teeth of carnivores tend to be either conical or triangular, in order to pierce flesh. More specifically, animals such as snakes, that swallow their food whole, tend to have conical teeth. Prey items can then be grabbed and held inside the mouth. However, carnivores such as sharks, which saw of chucks of meat to obtain food, have triangular teeth with serrations (4).
This quote also relates to the digestive system, as the oral cavity is the beginning of both physical and chemical digestion of food. In the oral cavity, ducts secrete saliva, which contains salivary amylase (2). This enzyme “hydrolyzes starch…and glycogen”. Ultimately, the mastication of food helps to amplify the process of the chemical digestion of carbohydrates in the mouth.
This excerpt also may be related to the evolution of human jaws and teeth. Because of the change in human diet from one that was course and abrasive to a softer more westernized palate, evolutionists have determined that the human jaw has grown smaller, creating less room for teeth. Ultimately, “evolution has produced an increase in brain size at the expense of jaw size” (1). Therefore, there is often less room in the mouth for the wisdom teeth, also known as the third molars. These teeth are now regarded as vestigial, as they are generally useless to those who have them.
Once again, Shubin is able to take a topic that may seem quite difficult to understand, such as the reasoning behind differences in the structure of organisms, and oversimplify it for the average person to understand. However, this excerpt fails to mention that there are numerous variances in structure between two organisms that are both carnivores or both herbivores, simply because of varying niches and food sources.
Works Cited
(1) "Are Wisdom Teeth (third Molars) Vestiges of Human Evolution?" Answers in Genesis - Creation, Evolution, Christian Apologetics. Web. 07 June 2010. < http://www.answersingenesis.org/tj/v12/i3/wisdomteeth.asp>.
(2) Campbell, Neil A., and Jane B. Reece. Biology. San Francisco: Pearson, Benjamin Cummings, 2005. Print.
(3) "The Comparative Anatomy of Eating." Vegsource.com. Web. 05 June 2010. http://www.vegsource.com/news/2009/11/the-comparative-anatomy-of-eating.html.
(4) "Teeth I: The Carnivores." Suite101.com. Web. 06 June 2010. <http://www.suite101.com/article.cfm/paleontology/40769/1>.
Post #4
"Like us, fish, lizards, and cows have bodies that are symmetrical with a front/back, top/bottom, and left/right. Their front ends (corresponding to the top of an upright human) all have heads, with sense organs and brains inside. They have a spinal chord that runs the length of the body along the back. Also like us, they have an anus, which is at the opposite end of their bodies from the mouth" (97).
This excerpt relates directly back to our dissection lab, where we determined the physical characteristics of animals, such as symmetry, cephalization, and tissue layers. We also focused on whether animals were coelomates or acoelomates- that is, whether or not they had a body cavity, as well as the structure of their digestive systems. These two final properties relate back to the mode of development of animals.
Animals may either develop as protostomes or deuterostomes. These modes are generally distinguished by three features- cleavage, coelom formation, and fate of the blastopore. In animals with protostomes development, such as an earthworm, a pattern known as spiral cleavage is often seen. This type of cleavage is often known as “determinate cleavage”, because the pattern of development may determine the development of the embryonic cell very early on. In contrast, animals with deuterostomes development, such as humans, tend to develop in a pattern known as radial cleavage. In this type of cleavage, which is indeterminate, “each cell produced by early cleavage divisions retains the capacity to develop into a complete embryo” (1). In both protostomes and deuterostomes, the digestive system begins as a pouch known as the archenteron. However, in protostomes, the mesoderm splits to form the ceolom. However, in deuterostomes the folds of the archenteron form the coeloms. Ultimately, the most distinguishable characteristic that differentiates protostome development and deuterostome development is the fate of the blastopore. The blastopore is “the indentation that during gastrulation leads to the formation of the archenteron” (1). After the development of the archenteron, another opening develops at the other end of the gastrula. These two openings become the mouth and anus of the organism. In protostomes, the blastopore becomes the mouth, while in deuterostomes, the blastopore develops into the anus.
In our phylogenetic trees, one of the indications for the evolution of organisms was deuterostomes versus protostomes. The animals that are acoelomates are also protostomes, while the animals that are coelomates are also deuterostomes. Animals with a coelom tend to be more “evolved” than those without one- these animals included the rat, snake, frog, and perch. Therefore, the connection can be made that deuterostome development generally leads to animals that are more evolved.
Only at this point in Niel Shubin's book have I started to appreciate his ability of relating science to daily life. My thought process prior to this moment was that Shubin's supposedly "scientific" explanations of animal structure and evolution were actually insufficient in their scientific support. However, I have come to the conclusion (finally!) that Shubin does a remarkable job at simplifying almost every topic in his book. The way he relates and appeals to the reader by stating "like us" makes it even simpler to understand these scientific concepts (although they're pretty simple in the first place)....Actually, now that I think about it, I think this guy should stick to digging up bones.
Works Cited
(1) Campbell, Neil A., and Jane B. Reece. Biology. San Francisco: Pearson, Benjamin Cummings, 2005. Print.
Post # 5
"When the finely tuned balance among the different parts of bodies breaks down, the individual creature can die. A cancerous tumor, for example, is born when one batch of cells no longer cooperates with others. By dividing endlessly, or by failing to die properly, these cells can destroy the necessary balance that makes a living individual person" (118).
The human body is a finely tuned machine, where every individual part must work in harmony in order for there to be proper function. However, as the excerpt above mentions, it is quite possible that very minor errors could lead to life altering (or even life ending) cell malfunctions. Cancerous activity in the body is caused by mutation- whether these mutations are just spontaneous genetics or the result of environmental influences (chemical carcinogens, X-rays, viruses, etc.) is up to “luck”. However, these mutations must occur in the somatic cells of the body, which divide and multiply by mitosis, rather than in gametes.
Cancer in the body may also be caused by specific cancer causing genes called Oncogenes. Normal cellular genes that “code for proteins that stimulate normal cell growth and division” (1) are known as Proto- Oncogenes. However, Proto-oncogenes may become cancer causing oncogenes because of various genetic changes that may lead to overproduction of a proto-oncogenes protein product, or problems “in the intrinsic activity of each protein molecule” (1). Once a cell undergoes transformation, and then evades destruction by the immune system, it may then form a tumor, which is a mass of these abnormal cells.
The results of any of these causes of cancer are density independent and anchorage independent cancer cells, with a loss of cell cycle controls (see video above for an excellent explanation of these two topics) . When cancer cells do stop dividing, they do not do so at the normal checkpoints of the cell cycle. However, cancerous cells (when provided with ample nutrients) are said to be immortal. For instance, the cancerous cells removed from Henrietta Lacks as a tumor containing stem cells have been reproducing since 1951. A tumor is considered benign when it remains at its original site, but it is malignant when it becomes invasive to other organs of the body as it travels by means of metastasis.
After reading this excerpt, and learning about the causes of cancer in depth, I have realized just how difficult it must be for scientists to research potential cures. The fact that there are so many causes of cancer (some of them probably still unidentified) must make it seem nearly impossible to find a cure. We all see foundations such as the Jimmy Fund in local supermarkets, asking for donations for cancer research, and many often walk by without donating even a dollar. Scientists must feel such pressure from society when they are searching for cures from diseases, especially when they are very common.
Works Cited
(1) Campbell, Neil A., and Jane B. Reece. Biology. San Francisco: Pearson, Benjamin Cummings, 2005. Print.